Electric resistance device.



W. H. KELLER.

ELECTRIC RESISTANCE DEVICE.

APPLICATION FILED JUNE 2. 1915.

1,240,457. Patented Sept. 18, 1917.

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WILLIAM H. KELLER, OF NORTON, VIRGINIA.

ELECTRIC RESISTANCE DEVICE.

Specification of Letters Patent.

Patented Sept. 18,1917.

Application filed June 2, 1915. Serial No. 31,643.

To all whom it may concern Be it known that I, WILLIAM H. KELLER citizen of the United States, and resident oi Norton, in the county of Wise and State of Vir inia, have invented certain new and useful lectric Resistance Devices, of which the following is a specification.

This invention relates to devices inter- T posed in electric circuits for producing resistance therein.

It has particular relation to that class o devices comprising reflexed grids wlnch have the greater part of their surfaces exposed to the atmosphere. The advantages of this class of structures are well known.

With cast iron grids, bosses for spacing the grids apart were readily formed on the grids when they were cast. T he cast iron rids however are extremely fragile and the Toss by breakage is very large.

The .lossby breakage can be removed by forming the grids of material such as steel which can be punched from a sheet of metal. This provides an inexpensive manner of forming the grid, and the material being inexpensive, it is practicable to make it in a plane sheet, and of such dimensions that, when firmly clamped, it will support itself in proper position without the necessity of providing strengthening ribs or other special construction of the grids. Further, these ribs, etc, operate against compactness by necessitating the placing of the grids at greater distances apart. When the grids are made in plane sheets (they not then having any spacing bosses) they may be separated by pieces interposed between them, such as washers threaded on the clamping rods, these washers being of conducting material where a connection is desired and of insulation where it is desired to insulate.

v I have found that where punched steel grids in plane shsets, as referred to, are employed, even if they are tightly clamped together at first, the heating and cooling incident to the use of the resistance causes the grids to work ldosc, so that sometimes the tips of the refiexed portions of one grid will fall over against an adjacent grid. This of course short circuits a portion of the resistance and detracts from the usefulness of. the devices. This condition of affairs can be remedied by tighteningup the clamping means from time to time, particularly dur-.

vice." It has been found however practically impossible to cause the operators to attend to this tightening of the grids with the results as noted.

This condition can be largely alleviated by placing the clamping means under a very high tension initially but this is liable to break the clamping rods unless they are of large size. The large size is objectionable however because it requires too much of the grids to be cut away in making passage for the clamping rods.

According to the present invention I keep the clamping rods within a reasonable size and insure that the grids shall not come in contact with each other even if they work loose, by providing insulating separating means at points removed from the clamping means, as for instance, at points of flexure. I further provide a grid wherein the separating means as described is provided and wherein the rcflexed portions of the grid are all of the same length. If any of the reflexed portions were shortened up to. make room for clamping or separating devices this would mean that there would have to be more bars in the grid and consequently a greater width of grid, for a given resistance.

The metal washers used as spacers and connectors between the grids are rendered specially liable to corrosion by reason of the increase and decrease of temperature during the use of the apparatus. This tends todecrease the elliciency of the contact which is liable to grow worse and worse as time goes on. It is a further object of the invention to provide improved connecting means between adjacent grids. This I do by making the connecting and spacing means of galvanized metal. This reduces the tendency to corrosion and presents clean contact surfaces to the grids.

Other objects of the invention will appear hereinafter.

In the accompanying drawings which illustrate the invention Figure 1 is the side view of a rheostat embodying the invention and Fig. 2 is a section on the line :22 of Tteferring to the drawings, the frame in which the grids are to be mounted comprise the end plates a and 1) between which extend the clamping bolts 0. rl and 6. having nuts outside the ends of the plates as shown. Between the plates are arranged grids The structure of the grid is shown est in Fig. 2, from which it appears that each grid comprises the reflexed portions 1, 2, 3, 4, 5 and 6, thus providing a long path for the current in going from one side of the grid to the other. At one end of each of the outside bars of the grid is a hole, through which the bolts 0 and (I pass, while at the middle of the grid upon the opposite side from the holes mentioned is another hole, through which is threaded the bolt e. The grids are ordinarily insulated from the bolts 11, r, and g, by insulating sleeves or bushings. as 7, S an'd9, whichenrelop. the bolts. The grids are spaced from each other on the clamping bolts by means of washers. These washers, as 10, 11, 12, and 13, may be of insulating material, it being desired to insulate adjacent grids from each other at these points, while washers, as 14, 15, 16 and 17 may be of metal, it'being desired to. electrically. connect the adjacent grids at these points. Where desired the metal washers may be extended into terminals as 18 and 19 for receiving the ends of the wires, by which external connections are to be made. Preferably the insulating bushings and washers referred to are made of mica, although other insulating material mi t be employed;

n order to insure that the grids are properly spaced apart, even though the tightemng of the clamping means may not be properly attended tating an undue magnitude of the clampin bolts, rods 20, 21, 22, and 23 are passer through holes in the grids at their points of ficxu'rc. These rods are insulated from the grids by insulating bushings 24, 25, 26 and 27 and carry insulating washers as 28, 29, 30 and 31 interposed between the grids. These rods '20, 21, 2'2 and 23 are much smaller than the clamping rods. They' serve to support the insulating wash-n ers which separate the grids, and ordinarilyhave sli ht, if any, clam in effect. They may be eld in osition y icing extended through the cut plates, outside of which nuts may he applied to them.

Each gridis punched from a sheet of steel of suitable thickness, and all the parts of' the punched grid lie in a plane sheet. Other forms of iron and steel may be employed but do notrealize all the advantages to the same extent as the. steel.

The metal washers interposed between the grids for making connections between the same, as before. referred to, are of galvanized metal, preferably steel. This insures against deterioration of the connection by corrosion and provides a good con tact surface. i

The end plates (1 and b may be provided to, and without neressiposed to the an, of means with feet 32 and 33, by means of which the rheostat may be bolted or screwed to a suitable support.

lVhat I claim is 1. In an electric resistance device, the combination with a plurality of reflexed resistance grids formed from sheet metal and of substantially uniform thickness throughout, and having the greater part of their surfaces exposed to the air, clamping means including rods extending transversely of the planes of said grids for clamping the grids together, means for insulating said grids from said clamping rods, metallic and insulating spacing members adjacent said clamping rods and interposed between adjacent grids, whereby the grids are spaced apart from one another, and whereby the grids are insulated from each other or electrically connected together at desired'points, rods extending transversely of the planes of said grids at points removed from said clamping rods, and carrying insulatin" pieces insulating the. grids from the rocl s and from each other, the said insulating pieces of different rods being separated and individual to each rod.

2. In an electrical resistance device, the combination with -a plurality of rellexcd resistance grids .having the greater part of their surfaces exposed to the air, clamping means including rods extending tmnsversely of the planes of said grids for clamping the grids together, means for insulating said grids from said clamping rods and from each other adjacent to said rods, and insulating separating means interposed between adjacent grids In an electrical resistance device, the combination with a plurality of refiexed resistance grids having the greater art of their surfaces exposed to the air, 0 means for clamping the grids together, comprismeans for insulating said grids from saidrods and from each other adjacent to said rods, rods smaller than the clamping rods passing through said grids at each point of tiexure, and carrying ins'ulation,,insulating the grids from each other.

4. In an i'lectl'l(:al resistance combination with a plurality of sistance grids inning of substantially the ing the greater part of their surfaces exfor clamping the grids together comprising 'clamlping rods extending through said grids, meansfor insulating said grids from said rods and from each other adjacent to said rods and rods passing through each point of flexure of said grids and carrying insulation, insulating the grids from each other.

In an electrical resistance device, the

same length, and havat each place of fiexure. 4

combination with a plurality of reflexed resistance grids having the greater part of their surfaces exposed to the air, the whole of each grid lying in a plane sheet, of means for clamping the grids together comprising rods extending alon said grids, means for insulating said gri s from said rods and from eac 1 other adjacent to said rods, rods extending along said grids at their points of ficxure, insulating bushings and washers carried by the last mentioned rods for insulating the grids from each other and washers carried by the clamping rods, the last mentioned washers being interposed between adjacent grids, being of metal where electrical connection is desired and being of insulation where it is desired to insulate the grids.

6. In an electrical resistance device, the combination with a plurality of reflexed resistance grids, having the greater part of their surfaces exposed to the air, the said 20 grids being punched from sheet steel and having the reficxcd portions of a grid of substantially equal length, of means for clamping the grids together, comprising rods extending along said grids, ings and washers on said clamping rods, grid connecting washers upon said clamping rods, rods smaller than said clamping rods pass-. ing through said grids at each point of flex ure and insulating bushings and washers 30 carried by the last mentioned rods.

Signed at Norton, in the county of Wise and Sta e of Virginia.

WILLIAM H. KELLER.

\Vitnesses:

H. G. GILMER, G. A. SMITH.

insulating bush- 25 

